Conventionally, coating of molded members which are molded by injection molding and the like has been conducted from the view point of improving design properties and surface protection, by a method wherein molded members is spray-coated and then crosslink of the resulting coated molded article is conducted through baking. However, in view of protection of working environment and protection of external environment against discharge of a volatile organic solvent, trials of eliminating a solvent such as a method which conducts a powder coating or the like have been made. Furthermore, there is introduced a method of laminating a colored sheet with a moldable resin, followed by integral molding.
As a laminated sheet having high-brightness mirror-like metallic luster, for example, there is known a laminated sheet obtained by dry lamination of an aluminum vapor-deposited polyethylene terephthalate film or polypropylene film. Japanese Unexamined Patent Application, First Publication No. Hei 5-111991 describes a laminated sheet comprising a dried and cured film layer of an acrylate-based emulsion which contains scaly aluminum particles having smooth surface.
These sheets originally have high-brightness mirror-like metallic luster. However, since the vapor-deposited surface has insufficient malleability and an ink layer is provided as a surface layer, when subjected to molding such as vacuum molding or in-mold molding, unevenness of luster arises after molding, luster decreases and the like, and thus mirror-like metallic luster was insufficient for molding.
Japanese Unexamined Patent Application, First Publication No. 2002-46230 proposes the use of a laminated sheet comprising an ink film formed with an ink obtained by dispersing metal thin film fragments in a binder resin varnish. According to this method, malleability and luster unevenness can be improved to some extent. However, although the laminated sheet can maintain apparent luster against molding, the binder resin included in a high-brightness ink used has not a functional group such as carboxyl group. Therefore, because of insufficient adhesion between very thin scaly metal thin film fragments and the binder resin, peeling tends to occur at the interface between the binder resin and the metal thin film fragments. Consequently, this laminated sheet has such a disadvantage that the ink layer is likely to cause peeling due to cohesion.
Therefore, for the purpose of improving adhesion between the binder resin and the surface of the pigment, the surface of the pigment has been subjected to a silane coupling treatment and an adhesion modifier comprising a low molecular material having a polar functional group such as carboxylic acid group or amino group has been mixed into the ink. However, sufficient effect was not exerted.
Therefore, a first object of the present invention is to provide a high-brightness ink which imparts high-brightness mirror-like metallic luster to the printed surface and can achieve high adhesion between metal thin film fragments and a binder resin. A second object of the present invention is to provide a laminated sheet which has high-brightness mirror-like metallic luster of the high-brightness ink film layer and also has excellent formability (malleability) enough to cause less decrease in luster against molding.